The present invention relates generally to electrolytic cells. In particular, the invention relates to multilayer thin-film electrodes with a special surface geometry, and electrolytic cells incorporating the same. The electrodes are advantageous, for example, for their ability to resist cracking and flaking of the thin-film structure under a wide range of operating conditions.
In earlier research, Miley et al. used flat stainless steel plates coated with multilayer thin films as electrodes for an electrolytic cell. Such experiments are described in G. Miley, H. Hora, E. Batyrbekov, and R. Zich, xe2x80x9cElectrolytic Cell with Multilayer Thin-Film Electrodesxe2x80x9d, Trans. Fusion Tech., Vol. 26, No. 4T, Part 2, pp. 313-330 (1994). In this prior work, alternating thin-film (100-1000) layers of two different materials (e.g. titanium/palladium) were employed. The materials were selected to maximize the differences in the Fermi energy levels between the layers. Then, according to the xe2x80x9cswimming electron layerxe2x80x9d (SEL) theory described in the referenced publication, a large electron density would develop at the interfaces between the layers, enhancing exothermic reactions at the interface region during electrolysis. However, in the reported experiments, the thin films flaked off of the electrode plates due to differential expansion of the thin-film layers, caused by differences in expansion coefficients of the metals employed during absorption of H or D via electrolysis and subsequent self-heating.
Recently, others have shown that electrolysis can be successfully carried out with a packed-bed electrolytic cell where small plastic pellets are coated with several micron-thick layers of different materials. See, e.g., U.S. Pat. Nos. 4,943,355; 5,036,031; 5,318,675 and 5,372,688. They state that the reason this is possible is that the plastic pellets allow some expansion of the metal coatings.
Other electrolytic cells have employed coated electrodes of various forms. For example, U.S. Pat. No. 4,414,064 entitled xe2x80x9cMethod For Preparing Low Voltage Hydrogen Cathodesxe2x80x9d discusses a co-deposit of a first metal such as nickel, a leachable second metal or metal oxide, such as tungsten, and a nonleachable third metal, such as bismuth.
In light of these prior efforts, there remains a need for an improved, thin-film (50-1,000-xc3x85-thick layers) electrode configuration, which is optimized according to SEL theory and which resists degradation during operation in an electrolytic cell. The present invention addresses this need.
Accordingly, one preferred embodiment of the present invention provides a concave-surface conductive article for use as an electrode, which includes an electrode substrate having at least one concave surface, and at least one thin-film conductive layer coated on the concave surface, so as to provide stability against flaking or cracking of the thin-film layer upon expansion. This conductive article can be provided in a variety of forms which incorporate the concave surface(s), for example, pellets, rods, cylinders, fibers, and the like. More-preferred conductive articles of the invention include a plurality of thin conductive film layers, for example with differing metals in adjacent layers, which have large differences in Fermi energy level and simultaneously allow strong hydrogen- or deuterium-absorption in the metal and also good diffusion of these species through the layers.
Another preferred embodiment of the invention provides a flake-resistant thin-film electrode for use in an electrolytic cell, which has an electrode substrate and a plurality of thin-film conductive layers on the substrate. Expansion joints are provided in the thin-film layers, so as to reduce flaking or cracking of the layers during heating or hydrogen-isotope-loading.
Another preferred embodiment of the invention provides a conductive article including at least two thin conductive film layers adjacent to one another, wherein materials in the thin films are selected to provide a substantial Fermi-level difference between the adjacent films, the materials also having diffusivity and solubility of hydrogenous atoms, whereby substantial concentrations of hydrogenous atoms can develop in the films, the materials further being selected to react to provide sets of complex nuclei favoring at least one of energy production and reaction products predominantly having higher or lower masses. For example, in regard to Fermi-level differences, the following combinations are illustrative: Pd/Ni (xcex94F=1.3 eV); Pt/Ni ((xcex94F=1.5 eV); Pd/Fe (xcex94F=0.9 eV); Pd/Zr (xcex94F=1.6 eV); Pt/Th (xcex94F=2.4 eV). As to complex nuclei formation, for example, the Pt/Ni combination would provide a set of reaction products centered around mass numbers A=25, 35, 95 and 155. The Pt/Th combination, illustratively, would favor lower mass numbers in this set, but would give higher energy production than the Pt/Ni combination.
The present invention also provides electrolytic cells which incorporate electrodes of the invention, and methods for operating the cells.
The invention provides electrodes with thin-film coatings which resist flaking and cracking under expansion and thus provide extended electrode lifetimes, and electrolytic cells and, methods incorporating such electrodes. The objective criteria for selection and metal profiles in the present invention are distinguished from those in much prior work in electrolytic cells. The present invention includes a preference for minimal interdiffusion of the metals at the interfaces, such that a locally high electron density (swimming-electron layer) occurs at interfaces due to the selection of metal pairs with large differences in Fermi energy levels. Further, significantly thinner coatings (hundreds of angstroms or less) are preferred in order to maximize the reaction rate of absorbed ions per unit volume. To achieve stable coatings of this type, design considerations, such as the concave surfaces or segmented expansion joints described in the present disclosure, are important.
Additional objects, features and advantages of the invention will be apparent from the description which follows.